Trains, busses, airplanes and Personal Area Networks (PANs) are examples of use cases where moving network technologies can be applied. A moving wireless network is a cluster consisting of Mobile Nodes (MNs) and Mobile Routers (MRs). A Mobile Router routes IP traffic between a Mobile Node and the Internet (or other IP network). The Mobile Router acts as an access point for the Mobile Node. A Mobile Router may be connected to another moving network or directly to the Internet via an access point (AP). In the former case, a set of nested mobile networks results. Figure lA illustrates a scenario where a Mobile Node is initially attached to a Mobile Router. In FIG. 1B, the Mobile Node is handed-off to a second Mobile Router, whilst in FIG. 1C the Mobile Node is handed-off from the second Mobile Router to a fixed access router.
A Mobile Router broadcasts beacons to advertise its existence and that it provides a mobile routing service. The beacons may contain an operator identifier, for example, to aid selection of an appropriate network by a user. When a Mobile Node finds a suitable Mobile Router, the Mobile Node triggers an attachment exchange with the Mobile Router.
It will be appreciated that when a Mobile Router changes its point of attachment to the Internet, or is handed-off to another Mobile Router, the locations (i.e. IP addresses) of all of the downstream Mobile Nodes will change. In order to maintain service continuity during and after hand-off of a Mobile Router, some mechanism is required in order to ensure that data sent from peer (or correspondent) nodes involved in a communication session with the Mobile Node is sent to the Mobile Node at the node's new location. A number of approaches are possible.
Firstly, the Mobile Node itself can be responsible for notifying the Peer Node(s) of its new location. This approach results however in a large volume of location update related signalling for even relatively small moving networks, and results in relatively long hand-off reaction times. A second approach involves the creation of a tunnel between the Mobile Router and some home router (or “home agent”) within the fixed network. All traffic sent from a Peer Node to a Mobile Node (and possibly traffic sent in the reverse direction) is routed through the tunnel. When the Mobile Router changes its location, it sends an update to the home router. Two problems with this approach are the use of sub-optimal (triangular) routing and the increased packet size due to the tunnelling overhead. An example of this second approach is the IETF Network Mobility (NEMO) mechanism. A third approach involves the delegation of signalling rights from the Mobile Nodes to the Mobile Router to allow the Mobile Router to send location update signalling to Peer Nodes on behalf of the Mobile Nodes.
An example of the third approach is described in WO03036916, where a Mobile Node generates an authorisation certificate by signing a public key of the Mobile Router with its own private key. The certificate is then provided to the Mobile Router, which includes the certificate in any location update message it sends on behalf of the Mobile Node. The message is also signed with the private key of the Mobile Router. Using the public keys of the Mobile Router and the Mobile Node, a Peer Node can verify both that the update relates to the claimed Mobile Node and that the Mobile Router is authorised to perform the update on behalf of the Mobile Node. A Mobile Router may further delegate responsibility to another (upstream) Mobile Router by signing the public key of the upstream router with its own private key, adding this to the certificate, and passing the certificate to the upstream router. This approach necessitates however that the Peer Node process a relatively long certificate chain for every received location update.